This invention relates to drilling devices for drilling holes in structural components, for example, those used in aircraft construction, and more particularly relates to a machine for drilling structural components at preprogrammed locations along the structural component.
The construction of an aircraft requires the assembly of a large number of structural components. Among those components are included the stringers which are elongate components attached to the metal sheeting that becomes the outer skin of the aircraft. To facilitate the mass production of aircraft it is desirable to prepare the stringers for attachment to the skin panels prior to the assembly of the skin panels to the aircraft frame members. A necessary operation in the construction is to attach clips to the stringers typically by means of rivets passing through holes drilled in the stringers and the clips. The clips form the interface between the stringer and the frame with the skin panels being riveted to the stringers. To facilitate construction it is desirable to pre-drill the holes in both the stringers and the clips prior to their attachment to one another and certainly prior to the time of final assembly of the skin to the frame. In order for pre-drilling to be effective, it is necessary both to accurately locate the holes in the stringers and to drill the holes perpendicular to the stringer surfaces so that the clips will be correctly aligned with their associated frame locations upon final assembly of the skin to the stringer.
A manual drilling fixture has been used to hold the stringer prior to its assembly to allow operators to drill by hand each of the four holes required for each clip location on the stringer. The manual drilling fixture requires that the operator manually clamp the stringer to the fixture and walk down both sides of the fixture placing a hand-held drill bushing in an appropriate locating bushing installed at each drilling location. Then, using the other hand, the operator inserts the drill bit through the drill bushing to drill the hole in the stringer. In order to ensure correct location of the holes in the stringer, the operator is required to exercise extreme care to assure proper stringer positioning in the fixture and also to exercise extreme care in determining which of the several possible combinations of clip location is to be drilled in any particular stringer. Also, due to the manual operation of the drill, wear in the drill bushings is severe and tends to cause hole elongation and thereby some stringer clip mislocation and misalignment. Corrections to the drilling must be made during final assembly when it is extremely awkward to reach certain locations where the clip must be attached to the stringer, thus, severely affecting the efficiency of construction.
It is therefore an object of the present invention to provide a machine for drilling stringers which allows precise indexing of the hole locations prior to final assembly of the stringer to the aircraft skin.
It is another object of this invention to provide such a machine in which the drilling location indexing is automatically programmed.
It is a further object of this invention to provide a stringer-drilling machine which allows accurate locating of the holes drilled in the stringer without regard to warp and bend of the stringer.
It is a further object of this invention to provide a stringer-drilling machine which provides feedback to the operator prior to the start of the drilling operation, informing the operator that correct indexing of the drilling location has occurred.